The invention disclosed herein relates to journaling machine parts for rotation and, by way of example but not exclusively, to rollers that are used in the inkers of printing presses and in machines for applying a thin coating on a web or sheet of material such as paper. Particularly, the invention is exemplified in providing tangentially contacting rollers with means for supporting the rollers for rotation and performing the additional functions of allowing the rollers to automatically adjust into perfect alignment with each other and also provide a path for forcing cooling air through the interior of the roller.
The rollers most widely used in the inkers of high speed printing presses, such as offset printing presses, have traditionally been formed of a solid metal cylinder having shafts extending from opposite ends so the rollers can be connected to means for driving them rotationally. One roller picks up ink from an ink reservoir and then there is a roller to roller transfer until the ink is finally coated on a rotating photolithographic plate. In the most commonly used inkers, means are provided for oscillating at least some of the tangentially contacting rollers axially in an effort to obtain more uniform distribution of ink on the rollers and, hence, on the printing plates. As is well known, ghosting or residual imaging of the printed material is a consequence of non-uniform distribution of the ink on the rollers that contact the image plates. Conventional presses use various mechanisms such as wobble plates and cams for oscillating certain of the rollers axially. Conventional oscillating mechanisms are bulky and have several moving parts which are subject to wear and other defects that are well known to those involved in the printing industry.
One of the problems that has not been solved satisfactorily until the invention described herein was made is the problem of getting the periphery of the tangentially contacting oscillating and non-oscillating rollers to contact each other uniformly along their entire lengths. Obtaining uniform contact of all the rollers in the inker when the press is being assembled for the first time is problematical in itself, but maintaining uniform line contact when the press is in operation is even more difficult because of thermal distortions. In high speed presses, the solid ink rollers become very hot because of friction between rollers which results from some of the rollers being driven rotationally and others being turned by frictional contact with those that are driven. When the solid rollers become hot, they have a tendency to warp or bow and assume different diameters along their length because of thermal expansion and warpage. This tends to make ink distribution on the rollers non-uniform. A possibly worse consequence is that the ink cannot be maintained at the proper viscosity. The ink gets thinner and thinner as the roller temperature increases. As the ink thins, the water vapor that is sprayed on the photolithographic image plates tends to emulsify the ink. The action of the ink on the plates then is such that areas that ought to print with a good solid color become mottled and ghosty. This reduction in printing quality can be discerned even by a layman who does not have the sensitivity to quality of an experienced printing press operator.
Some of the rollers in the inker of a high speed printing press will have a coating or outer sleeve composed of an elastomeric material such as rubber. When presses are run at near or above their ostensible rated speed, the heat generated in the roller is sometimes great enough to soften the rubber sleeve to the extent that it is bulged or expelled centrifugally from the underlying cylindrical metal roller. This, of course, requires shutting down the press and replacing the rollers.
Sometimes when presses are being stressed to their speed limit, air hoses or fans are set up to try to blow air over the rollers in the inker for cooling them to the extent possible. Pumping refrigerated water through certain of the rollers in an inker has also been tried. Adequate cooling has never been achieved by any of these practices.
U.S. Pat. No. 4,509,426, dated Apr. 9, 1985, discloses an oscillating roller wherein the oscillating mechanism is installed within the roller cylinder itself. This patent is owned by the inventor of the invention described herein. Its entire disclosure is incorporated herein by reference. An improved axially reversing roller for printing presses and sheet coating machines is also described in pending U.S. patent application Ser. No. 892,901, filed Aug. 4, 1986. The entire disclosure of this patent is also incorporated herein by reference.
The axially oscillating or reversing rollers described in these patents are not solid rollers, but are comprised of tubular cylinders of metal or plastic which are journaled for rotating and reciprocating axially on a fixed shaft. There is a cylindrical element fixed internally and coaxially of the roller cylinder. This element has an internal left hand thread contiguous with a right hand thread or helix. The roller is driven rotationally as a result of being in tangential contact with a rotationally driven roller. Axially spaced apart plungers having threaded followers are mounted on the stationary shaft within each of the internally threaded members. There is a left hand thread engaging follower on one plunger and a right hand thread engaging follower on the other. They are interlocked so that when one is driven into engagement with one internal thread, the other is forcibly disengaged from the cooperating internal thread. Thus, as the roller rotates with one thread follower engaged, the roller will shift axially. When it reaches a pre-determined limit, the striker element causes the engaged follower to become disengaged and the previously disengaged follower to become engaged with the thread of opposite twist so that the roller reverses and shifts axially in the opposite direction.
The axially oscillating roller just described in general terms is meritorious in that the oscillating mechanism is built in and requires no external drive other than the driving force from a driven tangentially contacting roller. For this and other reasons it became highly regarded in the printing industry quickly. The fact that it provides for greater axial travel in both directions as compared with the prior art oscillating mechanisms has been a significant factor in getting good ink distribution and, as a result, eliminating ghosting. The roller can easily be installed in existing presses to replace oscillating rollers and dispense with the usual complex oscillating mechanism. They can be substituted for solid non-oscillating rollers in inkers so that there are more oscillating rollers in the inker. This improves ink distribution. Most advantageous of all, the oscillating roller has permitted running the presses at much higher speeds than were heretofore permissible without increasing ghosting. Regardless of the better quality printing and higher productivity achieved with the new oscillating rollers, heating of the rollers due to friction still is a major factor in determining the maximum speed at which a press may be run.